By Lukie Pieterse, Potato News Today

A broad climate lens on pests and diseases – more generations of insects, new late blight and early blight patterns, emergence of “southern” diseases in new regions – plus the adaptation stories from farmers on the front line.

Climate change is not only burning crops at the surface. It is quietly reshaping the invisible world of spores, vectors and soil-borne pathogens that make or break a potato season. What used to be “once in a decade” disease years are turning up back-to-back. Insects are squeezing in extra generations. And diseases that once belonged firmly to somebody else’s climate are starting to show up in new regions.

For growers, agronomists and processors, this is no longer a distant risk. It is a live management problem: spray programs calibrated for yesterday’s weather, seed health rules written for older geographies, and labels that assume pest ranges that are already out of date.

This piece takes a broad look at how heat and humidity are redrawing the potato disease and pest risk map – and how farmers and their advisers are responding on the ground.

Changing baselines – from “normal seasons” to weather whiplash

The first shift is not any specific disease, but the climate backdrop itself. Across many potato regions, average growing-season temperatures are rising, nights are warmer, and humidity patterns are becoming more erratic. In many temperate regions, potato production is increasingly being shaped by higher mean temperatures, longer frost-free periods, and more intense rainfall events.

This volatility matters because most major potato pests and diseases are tightly tuned to temperature and moisture:

• Late blight thrives when leaves stay wet and temperatures sit in a cool to mild band.
• Early blight and several stem and tuber diseases are happier at warmer temperatures and under stress conditions.
• Insects like Colorado potato beetle, aphids, potato psyllid and potato tuber moth develop faster as temperatures rise, up to their own optima.

Global reviews point to a general expectation of higher pest risk in cooler and temperate production regions as the climate warms, especially where mild winters allow more survival and extra generations.

For growers, that translates into a simple, uncomfortable reality: the historic “rules of thumb” about when pressure starts, when it peaks, and which regions are safer are becoming far less reliable.

More heat, more generations – insect pests on the move

Insect pests are among the clearest early winners in a warmer world. Many species complete their life cycles more quickly at higher temperatures, which means more generations in a single season and more overlapping waves of pressure.

Colorado potato beetle is a textbook example. In parts of Europe and Russia, its range has expanded northward, while the number of generations per season has increased as growing degree days accumulate faster under warmer conditions. In regions where one generation was once the norm, two generations are now possible in warm years – significantly raising defoliation and resistance pressure on insecticides.

Aphid populations, which drive virus spread (PVY, PLRV and others), also benefit from milder winters and longer growing seasons. More surviving adults and earlier spring flights can push virus pressure into regions and altitudes that historically counted on “cold protection” to keep seed fields cleaner.

Potato psyllid and zebra chip tell a similar story. Zebra chip, caused by the bacterium associated with potato psyllid, was once confined largely to warmer parts of the southern United States, Mexico and Central America. Over the last 15 years, the psyllid and disease have become established in the U.S. Pacific Northwest, with growers and processors in Washington, Oregon and Idaho now investing heavily in monitoring and control. Warmer conditions and milder winters are expected to support continued northward expansion, potentially brushing new regions if vector introduction occurs.

Potato tuber moth, traditionally a major pest in tropical and subtropical regions, is also projected to expand into new temperate zones. Modelling work suggests a future increase in damage potential where the pest already occurs, along with a likely expansion into warmer temperate belts in the northern hemisphere.

For growers, this convergence of pests means:

• Higher baseline insect pressure almost every year.
• More overlap between species, complicating spray timing and product choice.
• Greater risk of resistance development as control programs intensify.

It is also nudging many seed and table growers in cooler zones to rethink any complacency they once had about being “too cold” for certain pests.

Humidity spikes and new late blight windows

Late blight remains the disease that keeps many potato growers awake at night, and climate change is giving it new room to manoeuvre.

Late blight risk is highly sensitive to leaf wetness and temperature. Modelling work suggests that, under many scenarios, the global average risk of late blight initially increases as temperatures warm, particularly in currently cooler zones, before potentially declining in some places if conditions become too hot and dry for sustained infection.

On the ground, patterns are already shifting:

• In northern Europe and Fennoscandia, late blight has been documented appearing earlier in the season in recent decades, with climate change and changes in Phytophthora infestans populations both implicated.
• In Canada, late blight risk is becoming more important in some regions that historically saw lower pressure, while other areas may see fewer “classic” blight years if summers trend hotter and drier.
• In East African highlands, late blight remains a major threat, with warmer, wetter conditions in some seasons pushing disease further into marginal zones and stressing already fragile smallholder systems.

The complication for growers is that it is not a simple story of “more blight everywhere”. Instead, they are dealing with:

• Longer or earlier infection windows in some regions, demanding more flexible spray programs.
• More intense, short disease bursts tied to extreme rainfall events.
• Changing local pathogen populations, including strains that may respond differently to fungicide groups.

In practical terms, the older habit of relying on calendar-based spray intervals and historical “blight dates” is becoming riskier. Disease forecasting models that incorporate real-time weather and longer climate trends are moving from optional to essential in many production systems.

Early blight, stress diseases and the warmer field

If late blight is the emblem of cool, wet risk, early blight sits at the warmer end of the spectrum. Alternaria species tolerate higher temperatures than late blight and often exploit plants that are stressed by heat, drought or nutrient imbalance.

As summers warm and heat waves bite harder, growers in many regions are reporting:

• Earlier onset of early blight symptoms.
• More severe defoliation on susceptible varieties, especially in fields where nutrition or irrigation are not tightly managed.
• Stronger interaction with other stressors, such as ozone damage or waterlogging earlier in the season followed by hot, dry finishes.

Warmer, wetter periods are also amplifying other stem and tuber diseases:

• Blackleg and soft rot complexes, including more aggressive bacteria, favour wet, warm soils and can be moved rapidly in waterlogged conditions.
• Silver scurf and black dot can gain an edge when canopies stay humid for longer and when tubers mature under warmer soil conditions.
• In storage, higher ambient temperatures raise the risk of condensation events, condensation-linked rots, and sprouting pressure if cooling capacity is limited.

The result is a subtle but important shift: even in years when late blight pressure is modest, the disease bill may still be high because of other pathogens thriving in warmer, more stressed canopies and soils.

“Southern” diseases heading north and uphill

One of the most worrying trends is the gradual appearance – or predicted appearance – of diseases that were historically confined to warmer or lower-latitude regions.

Bacterial wilt and brown rot, caused by Ralstonia solanacearum, illustrate this risk. The pathogen is traditionally associated with tropical and subtropical conditions and thrives at relatively high soil temperatures. Yet climate change is likely to expand its potential range into more temperate zones, including parts of northern Europe and North America, particularly where warmer soils and prolonged wet periods become more common.

Similarly:

• Potato tuber moth, once seen mainly as a threat in tropical and subtropical regions, is already present across much of Africa, Asia, Latin America and parts of Europe and is projected to expand in some temperate areas as conditions become more suitable.
• Zebra chip risk has evolved from a regional concern in the southern U.S. and northern Mexico to a serious issue in the Pacific Northwest and New Zealand, with further spread linked to the potato psyllid’s ability to survive in milder winters.

For high-latitude and high-altitude production zones that have long relied on “cold barriers” to keep such threats at bay, this is a significant strategic challenge. Seed systems, certification schemes and surveillance networks built on older assumptions will need to adjust rapidly if these diseases gain a foothold.

When labels lag behind the weather

As pests and diseases shift, registration labels, resistance guidelines and seed regulations can struggle to keep up.

Many fungicide and insecticide labels are based on efficacy and resistance data generated in specific geographies under historic climate conditions. When disease complexes change – for example, more Dickeya in blackleg cases, or new late blight lineages dominating epidemics – performance in the field may diverge from expectations.

At the same time:

• Products registered for certain pests in one region may be needed against those same pests in newly affected areas where labels do not yet reflect that risk.
• Thresholds and timing guidelines developed for earlier climates may underestimate pressure where insects squeeze in extra generations or where disease risk windows start earlier in the crop.

This gap between biology and paperwork is not an academic issue. It influences insurance coverage, processor protocols, audit outcomes and growers’ legal exposure. Regulators and industry bodies face the difficult task of revising labels and guidelines fast enough to keep pace with a moving target.

Farmers on the front line – adaptation in real time

While many of these changes are playing out in journals and modelling studies, growers are experiencing them at eye level in their fields and storages.

Across regions, adaptation is already under way:

• Tighter scouting and forecasting: Growers and agronomists are leaning more heavily on disease forecasting tools, local weather stations and high-frequency scouting. In some seed areas, routine virus and vector monitoring that was once “nice to have” is becoming standard practice.
• Adjusting varieties and planting windows: In parts of Asia, Europe and North America, there is growing emphasis on varieties with stronger resistance packages for late blight, early blight and virus, and on shifting planting dates to avoid peak heat or humidity windows.
• Strengthening seed health and rotations: Short, tight rotations that were marginally acceptable under lower disease pressure are increasingly recognised as too risky. Growers in several regions are expanding rotation lengths, tightening hygiene in seed handling, and looking harder at on-farm multiplication strategies that minimise exposure to new diseases.
• Rethinking storage design: As harvest windows collide more frequently with heavy rain and warm conditions, storage managers are revisiting ventilation capacity, dehumidification, air distribution, and emergency cooling strategies to keep tubers sound and reduce disease development after loading.

These are not headline-grabbing innovations. They are incremental shifts – a new weather station here, an extra virus test there, a slightly different harvest timing or storage airflow pattern. But taken together, they are the beginnings of a climate-aware disease and pest management culture.

Building a climate-savvy risk map for potatoes

All of this points to an uncomfortable but unavoidable conclusion: the traditional potato disease and pest risk map is being rewritten, and the industry’s mental map needs to catch up.

Several priorities are emerging:

• Regional risk mapping: More work is needed to translate global and national climate projections into practical, region-specific risk maps for late blight, early blight, bacterial wilt, zebra chip, nematodes, virus complexes and key insect pests. These maps need to be updated regularly and communicated in plain language.
• Surveillance and early warning: Seed systems and processing supply chains will have to invest more in surveillance for new pathogens and vectors at their expanding frontiers – from psyllids and tuber moths to novel Ralstonia races. That includes international cooperation, since these risks do not respect borders.
• Breeding and technology: Breeding programs are already working on varieties that combine heat tolerance with resistance to major pathogens, while digital tools and decision support systems are helping growers pick the right actions in narrower windows. These efforts will need sustained backing from public and private funders if they are to match the speed of climate and pest change.
• Policy and regulation: Registration frameworks, quarantine systems and certification rules will have to become more adaptive, integrating climate projections and range-expansion data when prioritising pests, approving products, or setting seed standards. Otherwise, labels and regulations will continue to lag behind real-world risk.

For growers, the message is not that potatoes have become unmanageable, but that the rules of the game are changing. Heat, humidity and new diseases are converging to redraw the risk map. The more quickly the industry aligns its forecasting, agronomy, breeding and policy tools with this new reality, the better chance farmers have to stay ahead of the curve and keep potatoes healthy in a climate that is anything but stable.

Sources for further reading

Climate change impacts on potato storage
https://pmc.ncbi.nlm.nih.gov/articles/PMC11011371/
Effects of climate change on plant pathogens and host resistance
https://www.sciencedirect.com/science/article/pii/S2773126X24000212
The effects of climate change on potato production and potato late blight in the Asia-Pacific region
https://www.apn-gcr.org/publication/the-effects-of-climate-change-on-potato-production-and-potato-late-blight-in-the-asia-pacific-region/
Climate change may have limited effect on global risk of potato late blight
https://pubmed.ncbi.nlm.nih.gov/24687916/
BLIGHTSIM: a new potato late blight model simulating response to climate change
https://pmc.ncbi.nlm.nih.gov/articles/PMC7459445/
Meta-analysis on criteria and forecasting models for potato late blight
https://www.mdpi.com/2077-0472/15/21/2242
Evaluation of the phenological synchrony between potato and Colorado potato beetle under climate change
https://www.sciencedirect.com/science/article/abs/pii/S0167880916301621
Study on the potential distribution of Colorado potato beetle under future climate scenarios
https://www.frontiersin.org/articles/10.3389/fevo.2021.786436/full
Climate range expansion of a major crop pest: Colorado potato beetle
https://link.springer.com/article/10.1134/S0013873814050017
Predicting the shifting geographic range of Ralstonia solanacearum under climate change
https://www.frontiersin.org/articles/10.3389/fpls.2025.1548640/full
QMRA of Ralstonia solanacearum in potato cultivation
https://www.sciencedirect.com/science/article/pii/S0048969723048064
Scientific review of the impact of climate change on plant pests
https://openknowledge.fao.org/handle/20.500.14283/bbcd04b0-89dd-45a8-9d7f-37818570a275
Research helping producers stay ahead of late blight disease with climate change
https://agriculture.canada.ca/en/science/story-agricultural-science/scientific-achievements-agriculture/research-helping-producers-stay-ahead-late-blight-disease-climate-change-and-new-disease-types
Potential impact of climate change on potato crops and their main pathogens and pests in the northern Andes
https://www.researchgate.net/publication/390344893_Potential_impact_of_climate_change_on_potato_Solanum_tuberosum_crops_and_their_main_pathogens_and_pests_in_the_Neotropical_region_of_northern_Andes

Author: Lukie Pieterse, Potato News Today